1. Field of Invention
The invention relates to a driving apparatus using an electric motor as a power source, and more particularly, to a shaft support structure in a driving apparatus.
2. Description of Related Art
In the case of an electric motor in an electric vehicle driving apparatus using an electric motor as a driving source or in a hybrid driving apparatus and the like (hereinafter generally called a driving apparatus) in which an engine (combustion engine) and an electric motor are used in combination, the motor is required to be smaller in size in view of energy-saving and space-saving. In view of this requirement, for example, Japanese Patent Application Laid-open No. H10-175455 discloses a technique for downsizing an electric motor of a driving apparatus in which a gear ratio of a power transmission system to the wheels is increased using a speed-reduction mechanism such as a counter gear, thereby increasing driving torque by the gear ratio.
When the gear ratio of the driving apparatus is increased as in the prior art, it is necessary to rotate the electric motor at high speed to meet the speed reduction ratio, and there is a problem that a drag loss of a bearing as shaft support means which supports a counter drive gear on an electric motor shaft is increased or the durability of the bearing is lowered due to the high speed rotation. In the driving apparatus of the prior art, no special consideration is given to the increase in bearing load. When the life of the bearing is shortened or a ball bearing having small drag loss is used, the bearing must be greatly increased in size to sufficiently enhance its durability.